J. Chem. Phys. 99, 3075 (1993)
The relation between the rotational viscosity γ1 of binary nematic mixtures and the different rotational diffusion constants Dri of their components was studied by a combination of director reorientation experiments with dielectric relaxation spectroscopy. Marrucci's theory for the viscosity of single component nematics can be applied when the weighted reciprocal rotational diffusion constants are averaged arithmetically. An explanation is given by considering the sum of the molecular frictional torques.